Bilateral cochlea removal alters neuronal turnover in the adult avian song system in regions underlying singing behaviors. The goals of the proposed research are 1) to identify the processes of neuronal turnover that are affected by cochlea removal and 2) to determine whether these cellular effects are due to sensory deprivation, specifically the absence of song-related auditory stimulation. Deafening may prolong neuron survival. By altering the timing of deafening and cell birthdating, we will evaluate the effects of deafening on new neuron survival. Deafening may also either decrease cell proliferation or decrease neuron survival during the first few weeks after formation. The proposed experiments will discern between these two hypotheses. Neurons that undergo replacement are found in a region that increases spiking activity in response to song-related auditory stimulation. By blocking song-related auditory stimulation in hearing birds we will determine whether song- related auditory deprivation is responsible for the effects of bilateral cochlear removal. Because neuronal activity is tightly linked to the complex, learned, behavior of song production, the relationship between auditory experience, cell turnover, and behavior can be well characterized in this system. The goal of this research is to identify the normal sensory requirements for regulating neuronal replacement. Insight into mechanisms regulating adult neurogenesis, incorporation, and cell death may be expected to contribute to our understanding of the basic rules governing the maintenance, modification, and perhaps repair of neural circuits. This research may ultimately prove useful in designing strategies to repair the adult human brain.